Android, remove custom button border

I used this selector code for my custom button (simple.xml)

  <?xml version="1.0" encoding="utf-8"?>

  <selector xmlns:android="http://schemas.android.com/apk/res/android">
      <item android:state_focused="true" android:state_pressed="false" android:drawable="@drawable/focused" />
      <item android:state_focused="true" android:state_pressed="true" android:drawable="@drawable/focusedpressed" />
      <item android:state_focused="false" android:state_pressed="true" android:drawable="@drawable/pressed" />
      <item android:d开发者_JAVA百科rawable="@drawable/defaultbutton" />
  </selector>

But on my ImageButton I don't know how to remove border. I want to show only my images not to show border around button.

Thanks

---

I replace

    <ImageButton android:id="@+id/imagebutton"
  android:src="@drawable/simple"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  />

with :

    <ImageButton android:id="@+id/imagebutton"
  android:background="@drawable/simple"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  />

And work

---

Set android:background rather than android:drawable.